Flexible coaxial cable and method of making same

ABSTRACT

A flexible coaxial cable having an inner conductor to which a dielectric is secured such as by fusion and a convoluted outer conductor formed from a strip helically wound conductor secured, such as by soldering, to a corrugated conductive member, with the helically wound portion being secured to the peaks of the corrugations. The outer conductor is locked to the dielectric by crimping solely in the valleys between the helically wound convolutions. The crimping is accomplished under controlled conditions to provide a predetermined characteristic impedance, such as 50 ohms, for the coaxial cable by means of the mechanical crimping. The crimped cable is temperature cycled in a temperature chamber so as to provide thermal stability for the coaxial cable.

United States Patent [191 Pete [451 Mar. 19, 1974 FLEXIBLE COAXIAL CABLE AND METHOD OF MAKING SAME Inventor: William T. Pote,-41 Moraine Rd.,

Morris Plains, NJ. 07950 Filed: July 13, 1972 Appl. No.: 271,607

US. Cl 29/593, 174/102 D. 174/106 D,

324/57 R Int. Cl. G05f 1/00 Field of Search 29/624, 203 C, 202.5, 593;

156/47, 50, 51, 52, 53, 54, 56; 174/102 R. 102 C, 102 D, 103, 104,106,107, 109; 324/57 R, 62-64 Primary Examiner-Charles W. Lanham Assistant ExaminerJoseph A. Walkowski Attorney, Agent, or FirmHubbe1l, Cohen & Stiefel; Lawrence G. Kurland [5 7] ABSTRACT A flexible coaxial cable having an inner conductor to which a dielectric is secured such as by fusion and a convoluted outer conductor formed from a strip he1ically wound conductor secured, such as by soldering. to a corrugated conductive member. with the helically wound portion being secured to the peaks of the corrugations. The outer conductor is locked to the dielectric by crimping solely in the' valleys between the helically wound convolutions. The crimping is accomplished under controlled conditions to provide a predetermined characteristic impedance, such as 50 ohms, for the coaxial cable by means of the mechanical crimping. The crimped cable is temperature cycled in a temperature chamber so as to provide thermal stability for the coaxial cable.

- 16 Claims, 9 Drawing Figures TIME DOMAIN REFLECTO- METER VCRIMPING MEANS- PAIENIEUM'R 19 M4 3797; 104 sum 1 OF 2 FIG. 2.

TIME DOMAIN 34 REFLECTO METER VCRIMPING MEANS 28 F'IG,

IO l llilfl TEMP.

TEMPERATURE CHAMBER FLEXIBLE COAXIAL CABLE AND METHOD OF MAKING SAME BACKGROUND OF INVENTION 1. Field of the Invention I The present invention relates to flexible coaxial cables and a method of making such a cable.

2. Description of the Prior Art Coaxial cables, such as for microwave transmission, have existed in the prior art for a considerable period of time. As technology has developed, a need for flexible coaxial cables whose electrical characteristics do not vary during flexure of the cable, such as in aerospace utilizations, has developed. In such utilizations, often the electrical characteristics of the cable are critical and any variation therein will yield unsatifactory transmissions via such cables. In order to increase the flexibility of prior art coaxial cables, corrugated outer conductors, such as disclosed in US. Pat. Nos. 3,582,536; 3,173,990 and 2,890,263 have been utilized..In addition, other prior art attempts of providing such flexibility have utilized a corrugated outer sheath for the cable rather than a corrugated outer conductor, such as disclosed in US. Pat. No. 3,002,047. Furthermore, this concept of a corrugated outer sheath has been utilized for standard electrical cables, as opposed to coaxial cables, where such cables are exposed to considerable flexure, such as disclosed in US. Pat. Nos. 2,348,641 and 2,995,616.

In order to ensure electrical stability for a coaxial cable, the relative location between the various portions of the outer conductor, the dielectric and the inner conductor must remain constant during flexure of the cable or the electrical characteristics may vary. Prior art attempts to ensure this stability have involved the locking of a corrugated outer conductor to the dielectric surrounding the inner conductor, such as disclosed in U.S. Pat. No. 3,173,990 wherein such inner conductor is a foam polyethylene. However, such prior art flexible coaxial cables do not have sufficient flexibility nor do they have sufficient temperature stability, which also affects the electrical characteristics. These prior art coaxial cables utilize either a tube which is crimped to provide a corrugated tube or form the outer conductor by means of helically winding a piece of conductive material, welding the adjacent pieces together to then form a tube and thereafter crimping alternate longitudinal portions so as to provide a corrugated tube. In both instances, the maximum pitch for the convolutions of the outer conductor is severely limited. In the first instance, this limitation is primarily due to rupture of the conductive tube if the crimps are too closely spaced together whereas, in the second instance, the limitations are primarily due to the inability to sufficiently control the thickness of the resultant tube which is formed as a thin enough material cannot be utilized to produce a high pitch. Since the higher the pitch of the convoluted outer conductor, the greater the flexibility of the coaxial cable, these prior art flexible coaxial cables have not been satisfactory where large degrees of flexure are required together with electrical and temperature stability over a wide range of flexure.

Furthermore, these prior art flexible coaxial cables have primarily been of the foam polyethylene or solid dielectric type whereas flexible coaxial cables utilizing spline dielectrics have not exhibited satisfactory electrical and temperature stability characteristics. These disadvantages of the prior art are overcome by the present invention.

SUMMARY OF THE INVENTION A flexible coaxial cable is provided having an inner conductor to which is secured, such as by fusion, a dielectric, such as a solid dielectric composed of Teflon, high density polyethylene, or polyethylene foam, or a spline dielectric, and an outer conductor which is preferably comprised of a corrugated conductive member to which a helically wound conductive member is secured, such as by soldering, at the peaks of the corrugations. The outer conductive member is mechanically crimped to the dielectric solely in the valleys of the corrugations so as to provide a predetermined characteristic impedance, such as 50 ohms, for the coaxial cable. The crimped outer conductor is thereby locked to the dielectric so as to maintain the relative positions between the various portions of the coaxial cable. If the dielectric is a spline dielectric, the outer conductor is crimped to the fins of the spline and locked thereto. The coaxial cable is preferably placed in a temperature chamber after the crimping of the outer conductor to lock it to the dielectric and provide the desired predetermined characteristic impedance and temperature cycled between predetermined extremes, such as minus 100 centigrade and plus 225 centigrade for Teflon or minus 60 centigrade and plus centigrade for high density polyethylene so as to thermally stabilize the coaxial cable and stress relieve the outer conductor. In this manner both electrical and temperature stability are provided for the flexible coaxial cable. If desired, such as if a Teflon dielectric is utilized, this process may be repeated a second time so as to increase the mechanical and temperature stability of the flexible coaxial cable.

In accomplishing the preferred method of the present invention, the core composed of the inner conductor and the surrounding dielectric is preferably inserted into the convoluted strip wound outer conductor, the initial inner diameter of the outer conductor being greater than the outer diameter of the core. The outer conductor is then crimped in the valleys existing between the convolutions so as to lock the dielectric to the outer conductor. During this mechanical crimping, the characteristic impedance of the coaxial cable is measured, such as by a time domain reflectometer, so as to stop the crimping procedure when the measured characteristic impedance reaches a predetermined value, such as 50 ohms. Thereafter, the coaxial cable is placed in a temperature chamber and temperature cycled such as by cooling the cable at a temperature of minus centigrade (for Teflon) or minus 60 centigrade for high density polyethylene) for approximately 2 hours and then heating the cable at a temperature of plus 225 centigrade (for Teflon) or plus 80 centigrade (for high density polyethylene) for approximately 2 hours.

As previously mentioned, this procedure of crimping and thereafter temperature cycling may be repeated to increase the mechanical and temperature stability of the coaxial cable, such as when a Teflon dielectric is utilized.

BRIEF DESCRIPTION OF DRAWING FIGS. 1 through 3 are diagrammatic illustrations of various steps in practicing the preferred method of the present invention;

FIG. 4 is a cross sectional view of a preferred embodiment of a flexible coaxial cable produced in accordance with the preferred method of the present invention;

FIG. 5a is a perspective view of a spline dielectric;

FIG. 5b is an end view of the dielectric shown in FIG.

FIG. 50 is a cross sectional view similar to FIG. 4 wherein a spline dielectric is utilized in place of the solid dielectric illustrated in FIG. 4;

FIG. 6a is a diagrammatic illustration of a flexible coaxial cable produced in accordance with the preferred method of the present invention having end connectors mountable thereon; and v FIG. 6b is a cross sectional view of a typical end-toend coupling of a pair of flexible coaxial cables of the type shown in FIG. 6a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings in detail and especially to FIGS. 1 through 3 thereof, the preferred method of the present invention for making a flexible coaxial cable, generally referred to by the reference numeral 10, shall be described and, various flexible coaxial cable configurations which may be manufactured in accordance with this preferred method shall be described.

In accomplishing the preferred method of the present invention, a core 12 is initially provided for the coaxial cable. The core 12 is preferably composed of an inner conductor 14 such as a solid copper center conductor illustrated in FIG. 1 or a braided conductor illustrated in FIG. 5c, which is surrounded by a dielectric, such as Teflon, high density polyethylene or polyethylene foam which is locked to the inner conductor 14 in conventional fashion such as by fusion. The configuration of the dielectric 16 may be foam, solid as illustrated by way of example in FIG. 1, or spline as illustrated in FIGS. 5a through St, or any other desired dielectric configuration. For purposes of explanation of the preferred method of the present invention, it shall be assumed that the configuration of the dielectric 16 is a solid dielectric as illustrated in FIG. 1. The core 12 which is readily available, is preferably cut to a length which is slightly longer than the desired end length of the resultant flexible coaxial cable 10. As shown in FIG. 1, an outer conductor 18 is also provided for the flexible coaxial cable 10. The outer conductor 18 preferably is composed of a corrugated main conductive member 20 which has been corrugated to produce peaks 22 and valleys 24 in the conductive member 20 at a predetermined pitch. A helically wound conductive strip 26 preferably composed of the same conductive material as the main conductive member 20 is preferably helically wound about the main conductor member 20 so as to have the strip wound conductor 26 be helically wound about the peaks 22 of the corrugated main conductive member 20. The conductor strip 26 is preferably secured to these peaks 22 such as by soldering so as to form a single unitary composite conductive member wherein the peaks 22 are accentuated by the helically wound strip 26 so as to increase the flexibility of the outer conductor 18. Such a strip wound outer conductor is preferably of the type commerically available from Cooperative Industries of Chester, New Jersey under the typical designations C8 of such a conductor having a 3/ l6ths inch nominal electrical outer diameter or H3 for such a conductor having a one quarter inch nominal electrical outer diameter, by way of example and not by way of limitation.

As will be explained in greater detail hereinafter, any desired pitch for the helically wound produced convolutions may be provided, the greater the pitch the greater the flexibility of the resultant flexible coaxial cable 10, the smaller the nominal size outer diameter for the outer conductor the greater the pitch, preferably. This outer conductor 18 is preferably also cut to the same desired length as that of the inner core 12. Most preferably, the initial outer diameter of the inner core 12 is slightly less than the inner diameter of the hollow outer conductor 18. The core 12 is inserted into the outer conductor 18 and aligned end to end. Thereafter, the composite cable containing the slidable inner core 12 and the outer conductor 18 is crimped in any conventional fashion by denting or crimping solely the valleys 24 existing between the peaks 22 associated with the convolutions of the strip wound conductor 26. Such crimping may be accomplished by wheels (not shown) which ride in the valleys 24, such as wheels which are one third the width of the valley 24, uniform pressure being applied to these wheels so as to uniformly crimp the valleys throughout the longitudinal extent of the outer conductor 18. This is illustrated by crimping means 28 and arrows 30 in FIG. 2. The crimping is to an outer diameter less than the original outer diameter of the dielectric 16 of the core 12, this original outer diameter being illustrated in FIG. 2 by dotted line 32, so as to lock the dielectric 16 to the outer conductor 18.

Preferably, the inner conductor of such a cable 10 is silver plated copper while the outer conductor is preferably a copper alloy.

Typically, by way of example the outer diameter of the dielectric 16 at the crimping points in the valleys 24 is varied between 15 and 20 mils where the core outer diameter is between mils and 122 mils and the outer conductor 18 inner diameter is 125 mils originally, such as for three sixteenths inch nominal outer diameter flexible coaxial cable. The mechanical crimping is preferably accomplished in accordance with the desired characteristic impedance of the resultant coaxial cable. In other words, the outer conductor is crimped, which varies the characteristic impedance of the cable 10, until the desired predetermined characteristic impedance, such as 50 ohms for conventional microwave transmission, is provided for the cable. In order to accomplish this, the characteristic impedance of the cable 10 throughout the crimping step is measured by conventional means such as a time domain reflectometer of the type manufactured by Hewlett Packard under Model No. 1415 and illustrated in FIG. 2 by reference numeral 34. When the desired characteristic impedance appears on the time domain reflectometer 34 then the crimping is stopped either manually or by conventional electrical or mechanical means. The crimped locked coaxial cable 10 is then preferably placed in a conventional temperature chamber 36 and is temperature cycled in a predetermined temperature range at the extremes thereof such as preferably between minus 100 centigrade and plus 225 centigrade for Teflon and minus 60 centigrade and plus 80 centigrade for high density polyethylene. Preferably, the cable is cooled at a temperature of minus lOO centigrade (for Teflon) or minus 60 centigrade (for high density polyethylene) for approximately two hours and is then heated at a temperature of plus 225 centigrade (for Teflon) or plus 80 centigrade (for high density polyethylene) for also approximately the same period of time of 2 hours. This provides temperature stability for the coaxial cable 10. I

As will be explained in greater detail hereinafter, if desired, such as for a Teflon Dielectric, the crimping step and temperature cycling step may be repeated to increase the mechanical and temperature stability of the resultant coaxial cable 10.

Now briefly summarizing the preferred method of the present invention, the method comprises the following steps: providing a core of predetermined length, the core containing the dielectric and the inner conductor, the core preferably being slightly longer than the desired end length of the cable; providing a hollow outer conductor of the same length and having an initial inner diameter which is slightly greater than the outer diameter of the core, the outer conductor comprising a hollow tubular corrugated member surrounded by a helically wound conductive strip which is secured to and is disposed about the peaks of the corrugations of the tubular member; slidably inserting the core into the outer conductor tubular member until the core is longitudinally centered within the outer conductor; crimping the valleys of the outer conductor for embedding the outer conductor in the core dielectric portion so as to lock the dielectric to the outer conductor; measuring the characteristic impedance of the resultant coaxial cable during the crimping step and controlling the crimping in accordance with said measurements so as to stop the crimping when a predetermined characteristic impedance for the cable is provided; and temperature cycling the resultant coaxial cable at atleast two different temperature extremes for a predetermined period of time.

Referring now to FIG. 4, a cross sectional view of a typical preferred coaxial cable produced in accordance with the preferred method of the present invention is shown. By way of example and not limitation, the cable 10 illustrated in FIG. 4 has a solid dielectric 16 and a solid inner conductor 14. As was previously mentioned, the dielectric 16 may be any dielectric material such as Teflon or a polyolefin such as high density polyethylene or polyethylene foam and the inner conductor 14 may be any desired conductor material such as silver plated copper. As illustrated in FIG. 4, the outer conductor 18 is preferably composed of a hollow tubular corrugated main conductive member 20 comprising a plurality of uniformly spaced peaks 22 and valleys 24 having a predetermined pitch and a helically wound conductor strip, preferably composed of the same material as the tubular member 20, and being wound so as to be disposed about the peaks 22 of the corrugated inner member 20 so as to increase the depth of the corrugations. Most preferably, the helical strip 26 is secured to the peaks 22 of the tubular member 20 by conventional means such as soldering and is preferably of the conventional type commercially available such as manufactured by Cooperative Industries, of Chester, New Jersey, under typical designations such as C8 for three sixteenths inch nominal electrical outer diameter and H3 for one quarter inch nominal electrical outer diameter.

As also shown in FIG. 4, the valleys 24 of the outer conductor 18 are embedded into the dielectric 16 which prior to such embedding had a uniform radial dimension about its longitudinal extent, as illustrated in FIG. 1. The embedded valleys 24 lock the dielectric 16 to the outer conductor 18 so that the radial dimensions of the inner and outer conductors l4 and 18 are fixed during flexing of the resultant coaxial cable 10 so that the electrical parameters associated therewith do not vary during such flexure. The outer conductor 18 as well as the strip wound conductor 26 are preferably composed of a conventional conductor material such as copper alloy.

Referring now to FIGS. 5a, 5b and 50, as was previously mentioned, the dielectric 16 may be any conventional dielectric configuration desired, the choice of configuration being primarily dependent on the desired electrical characteristics of the resultant coaxial cable 10. Thus, the dielectric configuration may be a solid as illustrated in FIG. 4, a foam, or a spline as illustrated in FIGS. 5a, 5b and 5c, or any other desired configuration. The spline dielectric configuration 16a is a conventional configuration having a central cylindrical core through which the inner conductor passes and a plurality of circumferentially spaced fins, preferably five in number 40, 42, 44, 46 and 48, as illustrated in FIGS. 5a through 50, each of the fins 40 through 48, inclusive, longitudinally extending the length of the inner cylindrical core portion 38 of the dielectric 16a and being uniformly spaced from the adjacent fins about the circumference of the inner core 38. The fins 40 through 48 and the inner core 38 are formed as a unitary spline construction by any conventional technique such as extrusion molding of the dielectric, such as where it is composed of a polyolefin.

As .also previously mentioned, the inner conductor 14 may be a solid conductor or a braided conductor comprising a plurality of conductive members. Such a conventional braided conductor 50 is illustrated in FIGS. 50 through 50.

Referring now to FIG. 5c, which is similar to FIG. 4, a typical preferred coaxial cable 10a having a core composed of a spline 16a dielectric such as illustrated in FIGS. 5a and 5b and a braided inner conductor 50 is shown which coaxial cable 10a has been produced in accordance with the preferred method of the present invention. The outer conductor 18 is preferably identical with that previously described with reference to FIG. 4 and identical reference numerals associated with identical parts previously described with reference to FIG. 4 are utilized in FIG. 50 and will not be described in greater detail hereinafter. Suffice it to say that the primary difference between the coaxial cable 10a illustrated in FIG. 50 and the coaxial cable 10 illustrated in FIG. 4 is that the valleys 24 of the outer conductor are preferably only embedded in the surrounding fins 40 through 48 inclusive of the dielectric 16a, only fin 40 and a portion of fin 44 being visible in the view of FIG. 50. Thus, preferably, the valleys 24 are not embedded in the inner tubular portion 38 of the dielectric 16a of core 12 but rather only in the surrounding fins 40 through 48.

Referring now to FIG. 6a, a typical preferred coaxial cable 10, such as illustrated in FIG. 4, produced in ac- 7 E'ciffiiihiuitfi the prfir'edmethod ofthe present invention is shown. Preferably, the helical wound conductor 26, as was previously mentioned, has a predeterminedpitch together with the corrugations. As shown 8 terconnect two such cablesfa good electrical connection is made.

By way of example, and not by way of limitation, some typical parameters associated with coaxial cables in FIG. 6a, preferably end caps or connectors 52 and produced in ccordanciviiiiiiEEfGEi'ihiiibdTf 54 are threadably mountable on the outer conductor the present invention are given below, assuming a pre- 18 by means of internal screw threads 56 and 58, redetermined characteristic impedance for the coaxial spectively, which threads have the same pitch as the cable of 50 ohms. Typical parameters for a coaxial strip wound conductor 26. Preferably, end ca 54 has cable produced in accordance with the preferred a first portion 60 which contains threads 58, an insula- 10 method of the present invention utilizing a foam polyt'or portion 62 and a second connection portior The ethylen die q r r s- CHART 1 Min. Max. Max. Imped- Pitch Max. bend Oper. Efi. opcr. Cutofi ance, convolu- Nominal size O.D radius, temp., dielectric voltage, Cap freq., ohms tions, 0 .D inches inches inches C. constant RMS mtL/ft GH normal inch i6, .210 1.00 90 1.50 1,200 32.0 :l:l 18 .325 1.62 90 1. 50 1, 600 25 19. 7 50:1:1 12

second connection portion 64 preferably has screw threads 66 on the outside thereof for connection to a connector of the type identical with connector 52 as Typical parameters for a coaxial produced in accordance with the preferred method of the present invention u tili z ing a Teflon solid dielectric are as followsz CHART 2 Min. Max. Max. Imped- Pitch Max. bend oper. Efi. oper. Cutofl ancc, convolu- Nominal size O.D radius, temp., dielectric voltage, Cap., freq., ohms tions, O.D inches inches inches C constant RMS put/ft GH normal inch will be described in greater detail hereinafter. 3 5

As illustrated in FIG. 6b, the inner conductor 14 is preferably of sufficient length so as to extend to a'point slightly less than the outermost edge of insulator por- Typical parameters for a coaxial cable produced in accordance with the preferred method of the present invention utilizing a high density polyethylene solid dielectric are as follows:

CHART 3 Min. Max. Max. Impcd- Pitch I Max. bend. oper. Eff. I oper. Cutofi' ance, convolu- Nominal size 0.D., radius, temp., dielectric voltage, Can, freq., ohms tions, 0.D., inches inches inches C. constant RMS ppL/it. GH. normal inch .210 1. 00 9O 2. 34 1, 900 30.8 27. 0 50:1; 5 18 325 1. 62 90 2. 34 3, 000 30. 8 17. 0 50:1; 5 12 385 1. 85 90 2. 34 5, 000 80. 8 13. 0 50. 5 12 .505 2. 55 9O 2. 34 7, 000 30. 8 9. 4 505:. 5 11 865 4. 37 90 2. 34 10, 000 30. 8 5. 5 50=|:. 5 8 1. 25 5. 13 9O 2. 34 12, 000 30. 8 4. 8 505:. 5 7

tion 62. Connector 52 preferably comprises a first connection portion 68 containing internal threads 56, an 50' insulator portion 70 and a second connection portion 72 having threads 74 on the interior thereof which are preferably of a pitch identical with the pitch of thread 66 and being of sufficient diameter so as to be threadably mountable on threads 66. Preferably, the inner 55 conductor 14 extends into the interior of connector 52 a distance less than or equal to the overall length of connector 52 and slightly beyond insulator portion 70 and is of sufficient, length so as to be mateable with the portion of the inner conductor 14 extending within a connector of the type similar to connector 54 as illustrated in FIG. 6b so that when a connector of the type of connector 52 is threaded onto a connector of the type of connector54 when utilized with coaxial cable 10 of the type produced in accordance with the preferred method of the present invention, such as to in- As was previously mentioned, the values given above are provided by way of example and not by way of limitation. While utilizing cables produced in accordance with the preferred method of the present invention, the radial spacing between the outer surface of the inner conductor and the inner surface of the outer conductor will remain constant when the cable is flexed or bent so as to provide electrical stability for the parameters associated with such a coaxial cable such as impedance, attenuation, VSWR, phase linearity, and phase versus temperature, the temperature stability being enhanced by the temperature cycling of the coaxial cable. Such a cable may be preferably utilized to transmit radio frequency signals although any other desired utilization of coaxial cable which may occur to one of ordinary skill in the art may be accomplished.

thereon it enhances the mechanical strengthand elec trical alignment of linked coaxial cables. Furthermore, by utilizing the strip wound conductor for the outer conductor of such a cable, the flexibility of the cable is enhanced, as a greater pitch and depth of convolution may be provided.

It is to be understood that the above described embodiments of the invention are merely illustrative of the principles thereof and that numerous modifications and embodiments of the invention may be derived within the spirit and scope thereof.

What is claimed is:

l. A method of making a flexible coaxial cable comprising the steps of providing a core for said cable, said core comprising an inner conductive member and dielectric means surrounding said inner conductive memher, said inner conductive member being located substantially along the longitudinal axis of said dielectric means, said dielectric means having-an outermost radial extent about said longitudinal axis; providing a flexible hollow outer conductive sheath of substantially the same extent as said core, said sheath having a longitudinal axis coextensive with said core longitudinal axis and an innermost radial extent about said longitudinal axis which'defines the innermost circumference of said hollow within said sheath, said sheath innermost radial extent being initially larger than said core outermost radial extent, said sheath comprising a corrugated portion having a plurality of peaks and valleys of predetermined pitch and a helically wound conductive strip disposed about said peaks and having a pitch equivalent to said predetermined pitch, said strip being conductively mounted on said peaks, said valleys defining said sheath innermost radial extent, said peak mounted strip defining the sheath outermost radial extent; inserting said core within said sheath until said sheath and said core are substantially coextensive; crimping solely said valleys so as to deform said dielectric means by embedding said valleys in said dielectric means so as to lock said dielectric means to said sheath, said sheath innermost radial extent defined by said valleys after said crimping being less than said core outermost radial extent; and measuring the characteristic impedance of said coaxial cable during said crimping for stopping said crimping when a predetermined value of said characteristic impedance is reached, whereby electrical stability is provided for said flexible cable.

2. A method in accordance with claim 1, further comprising the step of temperature cycling said crimped coaxial cable between at least a pair of predetermined temperature extremes for a predetermined I period of time at each of said extremes, whereby temperature stability is provided for said flexible cable.

3. A method in accordance with claim 2, wherein said dielectric means is Teflon and said temperature cycling step comprises cooling said crimped cable at a temperature of substantially -lOC. at one of said temperature extremes.

4. A method in accordance with claim 3, wherein said cooling step comprises cooling said crimped cable at lO0C. for approximately two hours.

5. A method in accordance with claim 3, wherein said temperature cycling step comprises heating said crimped cable at a temperature of substantially +225C. at the other of said temperatures extremes.

6. A method in accordance with claim 2, wherein said dielectric means is Teflon and said temperature cycling step comprises heating said crimped cable at a temperature of substantially +225C. at one of said temperature extremes.

7. A method in accordance with claim 6, wherein said heating step comprises heating said crimped cable at +225C. for approximately 2 hours.

8. A method in accordance with claim 2, wherein said method further comprises repeating said crimping step and said temperature cycling step, whereby said electrical and temperature stability are enhanced.

9. A method in accordance with claim 1, wherein said method further comprises the step of stopping said crimping when a predetermined value of said charactel istic impedance is reached.

10. A method in accordance with claim 9, wherein said method comprises stopping said crimping when a characteristic impedance of substantially 50 ohms is reached. I

11. A method in accordance with claim 1, wherein said dielectric means comprises a spline dielectric having a plurality of radially extending fins the extent of which defines said core outermost radial extent, said crimping step comprising deforming solely a portion of said fins so as to lock said dielectric means to said sheath.

12. A method in accordance with claim 2, wherein said dielectric means is high density polyethylene and said temperature cycling step comprises cooling said crimped cable at a temperature of substantially 60C. at one of said temperature extremes.

l3. A'method in accordance with claim 12, wherein said cooling step comprises cooling said crimped cable at 60C. for approximately 2 hours.

14. A method in accordance with claim 12, wherein said temperature cycling step comprises heating said crimped cable at a temperature of substantially +C. at the other of said temperature extremes.

15. A method in accordance with claim 2, wherein said dielectric means is high density polyethylene and said temperature cycling step comprises heating said crimped cable at a temperature of substantially +80C. at one of said temperature extremes.

16. A method in accordance with claim 15, wherein said heating step comprises heating said crimped cable at +80C. for approximately 2 hours. 

1. A method of making a flexible coaxial cable comprising the steps of providing a core for said cable, said core comprising an inner conductive member and dielectric means surrounding said inner conductive member, said inner conductive member being located substantially along the longitudinal axis of said dielectric means, said dielectric means having an outermost radial extent about said longitudinal axis; providing a flexible hollow outer conductive sheath of substantially the same extent as said core, said sheath having a longitudinal axis coextensive with said core longitudinal axis and an innermost radial extent about said longitudinal axis which defines the innermost circumference of said hollow within said sheath, said sheath innermost radial extent being initially larger than said core outermost radial extent, said sheath comprising a corrugated portion having a plurality of peaks and valleys of predetermined pitch and a helically wound conductive strip disposed about said peaks and having a pitch equivalent to said predetermined pitch, said strip being conductively mounted on said peaks, said valleys defining said sheath innermost radial extent, said peak mounted strip defining the sheath outermost radial extent; inserting said core within said sheath until said sheath and said core are substantiaLly coextensive; crimping solely said valleys so as to deform said dielectric means by embedding said valleys in said dielectric means so as to lock said dielectric means to said sheath, said sheath innermost radial extent defined by said valleys after said crimping being less than said core outermost radial extent; and measuring the characteristic impedance of said coaxial cable during said crimping for stopping said crimping when a predetermined value of said characteristic impedance is reached, whereby electrical stability is provided for said flexible cable.
 2. A method in accordance with claim 1, further comprising the step of temperature cycling said crimped coaxial cable between at least a pair of predetermined temperature extremes for a predetermined period of time at each of said extremes, whereby temperature stability is provided for said flexible cable.
 3. A method in accordance with claim 2, wherein said dielectric means is Teflon and said temperature cycling step comprises cooling said crimped cable at a temperature of substantially -100*C. at one of said temperature extremes.
 4. A method in accordance with claim 3, wherein said cooling step comprises cooling said crimped cable at -100*C. for approximately two hours.
 5. A method in accordance with claim 3, wherein said temperature cycling step comprises heating said crimped cable at a temperature of substantially +225*C. at the other of said temperatures extremes.
 6. A method in accordance with claim 2, wherein said dielectric means is Teflon and said temperature cycling step comprises heating said crimped cable at a temperature of substantially +225*C. at one of said temperature extremes.
 7. A method in accordance with claim 6, wherein said heating step comprises heating said crimped cable at +225*C. for approximately 2 hours.
 8. A method in accordance with claim 2, wherein said method further comprises repeating said crimping step and said temperature cycling step, whereby said electrical and temperature stability are enhanced.
 9. A method in accordance with claim 1, wherein said method further comprises the step of stopping said crimping when a predetermined value of said characteristic impedance is reached.
 10. A method in accordance with claim 9, wherein said method comprises stopping said crimping when a characteristic impedance of substantially 50 ohms is reached.
 11. A method in accordance with claim 1, wherein said dielectric means comprises a spline dielectric having a plurality of radially extending fins the extent of which defines said core outermost radial extent, said crimping step comprising deforming solely a portion of said fins so as to lock said dielectric means to said sheath.
 12. A method in accordance with claim 2, wherein said dielectric means is high density polyethylene and said temperature cycling step comprises cooling said crimped cable at a temperature of substantially -60*C. at one of said temperature extremes.
 13. A method in accordance with claim 12, wherein said cooling step comprises cooling said crimped cable at -60*C. for approximately 2 hours.
 14. A method in accordance with claim 12, wherein said temperature cycling step comprises heating said crimped cable at a temperature of substantially +80*C. at the other of said temperature extremes.
 15. A method in accordance with claim 2, wherein said dielectric means is high density polyethylene and said temperature cycling step comprises heating said crimped cable at a temperature of substantially +80*C. at one of said temperature extremes.
 16. A method in accordance with claim 15, wherein said heating step comprises heating said crimped cable at +80*C. for approximately 2 hours. 